Effectiveness of Internal Family Systems Therapy in Improving Mental Health in Individuals With Borderline Personality Disorder

Brief background and rationale: Borderline personality disorder (BPD) is a chronic and disabling psychiatric condition marked by pervasive affective instability, identity disturbance, interpersonal dysfunction, and impulsivity. It affects approximately 1-2% of the general population and up to 20% of psychiatric populations, contributing substantially to healthcare utilization, suicide risk, and long-term disability. Existing evidence-based psychotherapies for this condition, such as dialectical behavior therapy, mentalization-based therapy, or schema therapy show significant benefits but these are modest and these interventions are quite resource-intensive. There remains a need for additional, theoretically grounded treatments that target core pathomechanisms of BPD-particularly emotion dysregulation, shame, and self-fragmentation.

Objectives: The primary objective of this pilot study is to assess preliminary effectiveness of internal family systems (IFS) therapy in reducing BPD symptom severity from baseline to post-treatment. Secondary objectives are to evaluate changes in emotion dysregulation, shame, self-compassion, interpersonal functioning, depression, anxiety, addictive behaviors and overall well-being; as well as to assess feasibility (recruitment, retention, adherence), acceptability, and safety. It is hypothesized that participants will demonstrate at least small-to-moderate improvements in BPD symptom severity, with congruent changes across secondary outcomes. Although clinical interest in IFS has grown exponentially in the past decades, empirical evaluation remains limited, and no studies to date have specifically examined its use in any personality disorder. Given the strong theoretical fit between IFS principles and BPD phenomenology, a structured pilot investigation is warranted to establish feasibility, safety, and preliminary effectiveness prior to larger controlled trials.

Study design: The study will use a single-group, repeated-measures design with assessments at baseline, 4 months, 8 months, and post-intervention (12-15 months). A target sample of fifteen adults will be recruited. Inclusion criteria are age 18 or older, sufficient English proficiency for participation, and a formal BPD diagnosis confirmed by a referring clinician. Exclusion criteria include active psychosis or mania, cognitive impairment, inadequate English comprehension, or participation in another form of psychotherapy during the study period.

Intervention: Internal family systems therapy, developed by Richard Schwartz, is an integrative psychotherapy that conceptualizes the mind as a system of subpersonalities ('parts') organized around a compassionate, stable core Self. The approach promotes internal harmony through increasing awareness, acceptance, and cooperation among these parts and the Self. Participants will receive weekly, one-hour IFS therapy sessions in the private mental health care setting over approximately 12 to 15 months. Treatment will be delivered by two licensed mental health professionals trained in the IFS model. Participants will pay a significantly subsidized session fee to reduce financial burden of participation in the intervention.

Outcomes: The primary outcome is BPD symptom severity measured by the Borderline Symptom List-23 and its supplement. Secondary outcomes include validated measures of emotion dysregulation (DERS-18), shame and guilt (GSQ-8), self-compassion (SCS-SF), interpersonal functioning (EXIS.pers), depression (PHQ-9), anxiety (GAD-7), addictive behaviors (SSBA-G), and well-being (WHO-5). Feasibility and acceptability will be evaluated through attendance, retention, and brief structured questionnaires.